Browsing by Author "Bridgeman, Philippe"

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    Numerical analysis of heat transfer and fluid flow in multilayer deposition of PAW-based wire and arc additive manufacturing
    (Elsevier, 2018-04-05) Bai, Xingwang; Colegrove, Paul A.; Ding, Jialuo; Zhou, Xiangman; Diao, Chenglei; Bridgeman, Philippe; Hönnige, Jan Roman; Zhang, Haiou; Williams, Stewart W.
    A three-dimensional numerical model has been developed to investigate the fluid flow and heat transfer behaviors in multilayer deposition of plasma arc welding (PAW) based wire and arc additive manufacture (WAAM). The volume of fluid (VOF) and porosity enthalpy methods are employed to track the molten pool free surface and solidification front, respectively. A modified double ellipsoidal heat source model is utilized to ensure constant arc heat input in calculation in the case that molten pool surface dynamically changes. Transient simulations were conducted for the 1st, 2nd and 21st layer depositions. The shape and size of deposited bead and weld pool were predicted and compared with experimental results. The results show that for each layer of deposition the Marangoni force plays the most important role in affecting fluid flow, conduction is the dominant method of heat dissipation compared to convection and radiation to the air. As the layer number increases, the length and width of molten pool and the width of deposited bead increase, whilst the layer height decreases. However these dimensions remain constant when the deposited part is sufficiently high. In high layer deposition, where side support is absent, the depth of the molten pool at the rear part is almost flat in the Y direction. The profile of the deposited bead is mainly determined by static pressure caused by gravity and surface tension pressure, therefore the bead profile is nearly circular. The simulated profiles and size dimensions of deposited bead and molten pool were validated with experimental weld appearance, cross-sectional images and process camera images. The simulated results are in good agreement with experimental results.
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    A three-dimensional wire-feeding model for heat and metal transfer, fluid flow, and bead shape in wire plasma arc additive manufacturing
    (Elsevier, 2022-09-19) Chen, Xin; Wang, Chong; Ding, Jialuo; Bridgeman, Philippe; Williams, Stewart
    A three-dimensional wire-feeding model has been developed to study the transient coupling behaviour of heat and metal transfer, fluid flow, and solidified bead shape in wire plasma arc additive manufacturing (WPAAM). A novel surface heat source model considering the arc energy shading effect is proposed and adopted. An improved momentum source of the arc force considering the arc pressure shading effect is also developed and used. This model has been used to study the metal transfer dynamics, flow patterns, and bead shape of the WPAAM process with a wire-feeding speed (WFS) of 1–5 m/min. The simulated results agreed reasonably with the experimental data. As the WFS increased from 1 to 5 m/min, three different metal transfer modes were observed, which changed from globular droplet mode to droplet-liquid bridge mode and solid-liquid bridge mode. Detailed metal transfer information was analysed, including metal transfer position, shape, average temperature, and main driving force. The effects of the arc shading and metal transfer on the melt pool dynamics and bead shape were simulated and discussed. A periodic flow pattern of the melt pool produced by the metal transfer impact causes ripples or even humping defects. As the WFS increased, the melt pool depression gradually disappeared due to the arc pressure shading effect. When the WFS increased to 5 m/min, a temperature drop of about 140 K in the central melt pool, caused by the arc energy shading effect and cold metal transfer, weakened the lateral flow significantly, which explained the decrease of bead width at a large WFS. The results demonstrate that the developed wire-feeding model and findings could be used as a theoretical tool and basis to better understand the underlying physical mechanisms and achieve bead shape control in the WAAM process.